1. Field of the Invention
This invention relates to a blowing apparatus whose suction passage is not linear, to a suction panel thereof, and to a straightening guide thereof.
2. Discussion of the Related Art
In some blowing apparatuses such as ventilating fans and ventilating systems, the suction passage extending from the suction port to the fan suction port of the blower is not linear. That is, the suction port is disposed at a position out of the front of the suction port so that the inner structure of, e.g., the blower cannot be seen from the suction port. The suction port is generally formed at a suction panel that constitutes the front of the blowing apparatus. The suction panel itself tends to be flat in structure to improve the design of the blowing apparatus.
Blowing apparatuses of this type are disclosed by, e.g., Japanese Utility Model Unexamined Publications Nos. Hei 4-113843, Hei 2-538, and Sho 59-49827. Each of these apparatuses has such a basic structure as shown in FIG. 17. In FIG. 17, a main body frame 1 that is of a rectangular box type with one open surface is divided into two sections, a suction chamber 4 and a blower chamber 5, by an opening 2 and a suction partition 3 that extends in parallel with the opening 2. A motor 6 is mounted substantially in the middle of a surface of the main body frame 1 which is opposed to the opening 2. A multiblade fan 7 is attached to the rotary shaft of the motor 6. The multiblade fan 7 rotates inside the blower chamber 5. Substantially in the middle of the suction partition 3 is a fan suction port 8, which is not only circular so as to be coaxial with the multiblade fan 7 but also bell-mouthed. The fan suction port 8 is open to the suction chamber 4. Further, a blowout port 10 communicating with a blowout passage 9 is formed in one side of the blower chamber 5. A piping member 11 installed in the ceiling is connected to the blowout port 10.
The main body frame 1 is fixed so that the opening 2 is generally flush with the ceiling surface of the ceiling plate. A suction panel 12 is attached to the opening 2, which faces the ceiling surface, by a fastening means such as a spring so as to close the opening 2. The suction panel 12 has slit-like suction ports 13 formed in the vicinity of the outer edge portions thereof that do not confront the fan suction port The slit-like suction ports 13 communicate with the suction chamber 4 and extend along the four sides or two opposing sides of the suction panel 12. Therefore, the front of the fan suction port 8 is concealed by a front panel portion 14 of the suction panel 12 so as not to be seen from outside. The suction chamber 4 is formed of a space enclosed by the rigid body surfaces including the inner peripheral surfaces of the main body frame 1, the suction partition 3, and the suction panel 12, and constitutes a suction passage 15 that extends from the suction ports 13 to the fan suction port 8 via the suction chamber 4 in nonlinear form.
Since the main body frame 1 and the suction chamber 4 usually must have an appropriate area as a suction passage or blowout passage, the sectional area thereof is set to a value about 3 to 6 times the opening area of the fan suction port 8. If the height of the suction chamber 4 (H in FIG. 17) is too small, the suction chamber 4 is subjected to pressure losses and cannot absorb the inertia of a rapid stream from the suction ports 13, thus having difficulty turning the stream toward the fan suction port 8. Hence, the height is set to a value at least about 30 to 60% the diameter of the fan suction port 8. On the other hand, the area of opening of the suction ports 13 is set to a value as small as possible so that design requirements can be met. The area is set to a value approximately equal to or up to twice the area of opening of the fan suction port 8. Therefore, the suction passage 15 extending from the suction ports 13 to the fan suction port 8 via the suction chamber 4 expands suddenly at the suction chamber 4 from the narrow suction ports 13, and then narrows again at the fan suction port 8, making itself nonlinear.
Also, another type of blowing apparatus is disclosed in Japanese Patent Unexamined Publication No. Hei 5-126378. As indicated by the chain line in FIG. 17, an umbrella-like guide member 16 made of a noise insulating material is provided on the back of the suction panel 12, so that not only the stream to the fan suction port 8 can be guided, but also fan noise propagated from the fan suction port 8 to the front panel portion 14 can be reduced.
A blowing apparatus having the similarly nonlinear suction passage 15 from the suction ports 13 to the fan suction port 8 via the suction chamber 4 is disclosed in Japanese Utility Model Unexamined Publication No. Hei 1-125897. This blowing apparatus is constructed, as shown in FIG. 18, so that the main body frame 1 is of a box type having no opening. The suction port 13 that is connected to the piping member 11 is formed on a side opposite to the blowout port 10. Therefore, there is no suction panel, and the suction chamber 4 is formed into an L-shaped space enclosed by the inner peripheral and bottom surfaces of the main body frame 1 and the outer surface of the blower chamber 5. The suction passage 15 suddenly expands at the wide suction chamber 4 from the narrow suction port 13 and narrows again at the fan suction port 8, similarly making itself nonlinear.
Any of the above-mentioned blowing apparatuses sucks air from the suction port or ports 13 to the fan suction port 8 via the suction chamber 4 by the rotation of the motor 6. At this time, the rapid stream introduced from the narrow suction port or ports 13 is decelerated upon entrance into the suction chamber 4, having the inertial effect thereof lessened. Therefore, the flow of the stream becomes dependent on the sucking force produced at the fan suction port 8, leaving itself sucked into the fan suction port 8.
In the conventional blowing apparati thus constructed, the suction chamber 4 shown in FIG. 17 expands suddenly and, therefore, the stream introduced into the suction chamber 4 is not decelerated uniformly, but flows while picking up air within the suction chamber 4. As a result, the direction of the stream is not steady, which eventually makes the stream extremely disturbed as shown by the arrows in FIG. 17. Such disturbed stream is converged at the fan suction port 8 within a short range in the floating direction, leaving the stream running into the multiblade fan 7 in an unstraightened condition, thus, aggravating the turbulence of the stream in the multiblade fan 7. This results in large fan noise. Further, the umbrella-like guide member 16 straightens the stream on the suction side to some degree, but the straightened stream is such that only some parts of the multiblade fan 7 can function, thus impairing blowing efficiency. In addition, the level of noise insulation is not more than what is implemented by the guide member 16.
Because the suction chamber 4, including the blowout passage 9 is enclosed by rigid body surfaces, repetitive reflections of sound waves of noises echo between opposing rigid body surfaces, the causing a standing wave (which is a sound whose frequency is determined by the form and size of the chamber, i.e., resonance). Since the fan noise that becomes a source for causing resonance is so large, as described above, the resonance is also large. FIG. 19 shows the frequency spectra of the noise produced by the blowing apparatus shown in FIG. 17. An high-level acoustic resonance is generated at 500 Hz and 1 kHz, and a low-level acoustic resonance is generated between 2 and 3 kHz.
The above-mentioned problem is addressed likewise in the blowing apparatus shown in FIG. 18 in which the flow passage of the suction chamber 4 is relatively long. However, the blowing apparatus shown in FIG. 18 is characterized in that the suction chamber 4 has a right-angled corner and there is only one suction port 13 which is unevenly distributed in one direction with respect to the fan suction port 8. These factors contribute to increasing the turbulence of the stream in the suction chamber 4 and aggravating the stream flowing into the multiblade fan 7.